Planing = equivalent of an aeroplane breaking the sound barrier
How planing works
Normally a non-planing, displacement, hull is restricted in its maximum speed by a formula related to its overall length
where HSPD (in knots) is maximum hull speed, and LWL is the hull length in feet at waterline. This speed is maximised when the boat sits between the bow and stern waves, with no intervening self-caused waves along its length.
At low speeds, a hydroplaning hull acts as a displacement hull. But, when the speed increases the hull begins acting as a planing hull. However, when the boat begins to plane the formula becomes irrelevant since the boat is climbing its own bow-wave. The bow rises slightly as it starts by mounting its own bow wave. When it reaches the speed where it overtakes the bow wave, the bow resumes its normal attitude. The boat can often be seen to leave its stern-wave some distance behind it. The hull is now planing.
Beginning to plane is the aquatic, and less dramatic, equivalent of an aeroplane breaking the sound barrier. The aeroplane at Mach 1 begins to pierce and go beyond its own ‘bow wave’, i.e. the compressed layers of air on its front surfaces and ahead of it.
A hydroplaning hull travels faster and more efficiently than a displacement hull of comparable size due to two factors:
less area of the hull is in contact with the water. This reduces the friction on the hull caused by water.
the hull is displacing less water from its path. Water is relatively heavy and a displacing hull must displace its own weight of water.
The characteristics of a planing hull are that it is narrow at the prow, with a broader beam towards the rear. The shape of the underneath of the rear of a larger, planing, powerboat is often V shaped. To plane, the power to weight ratio must be high; sailing boats need a good sail area and powerboats need a highly powered engine.
Note that under some high wind conditions, very light craft (such as windsurfers and kitesurfers) can actually be pulled up onto the surface of the water, or into the air, by the upward lift of the sail alone. Although this certainly reduces water resistance, it is probably better described as flying, rather than hydroplaning. It is also not a sustainable state, as sailing (or kite flying) involves the extraction of energy from the shear force between the wind and the water. If the entire hull leaves the water, the craft will quickly come to rest relative to the wind, and lose its lifting/driving force.
Där ser man. Någon annan som har en bättre förklaring?
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